In fact it's very simple, and you will learn how to send messages to their friends as soon as you start to work with ICQ. If you want to write something to the recipient in your contactlist, proceed as follows.
Find his nick in the list and click on it twice with the left mouse button. The second way to open a message window – click on the nickname of the addressee, right-click and in the popup context menu select "Send message" (Send message).
On the screen you will see a square message box, divided in the middle by a horizontal line. In the upper part of this window you will see the message of his companion and sent their phrase, and at the bottom you will directly to write.
After the message is written, you can send it two ways: with the button "Send" (Send), located in the lower right corner of the message window, or combination of keys. Typically, the hot key is used or a combination of right Ctrl-Enter or double-click the Enter button. In both cases, your message will be sent and you will see it in the top of the window.
If you need to send a message to several recipients at the same time, in order not to duplicate the same effect, as follows. Look at the "Send" button in the message window and you will see left a little window with an arrow. Click the cursor on it, you'll see a context menu with options: "Send current", "Send all, Send to all those in the network", "custom send". Select the desired option and click it. Your message will be sent to selected recipients.